feat(browser)!: Report web vitals for bfcache restores by default - #24325
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feat(browser)!: Report web vitals for bfcache restores by default#24325logaretm wants to merge 2 commits into
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logaretm
added this pull request to stack #24274
September 10, 2026 18:55
Renames the `webVitals.bfcache` option to `bfcacheNavigations`, which reads as the sibling of `softNavigations` that it is, and turns it on so a restore is measured like any other page view. Neither the option nor its predecessor has appeared in a release, so nothing needs a deprecation. Restores stay a distinct population, tagged `browser.navigation.type: bfcache` so they can be read apart from page load vitals rather than pooled with them. Fixes the attribution while enabling it: the restore's navigation span was remembered by matching on that same `bfcache` navigation type, which the restore's own web vital spans also carry, so the first vital replaced the navigation span and every later one hung off a sibling vital instead. In practice CLS, which is only finalized on pagehide, was parented to the LCP span. The existing unit tests could not catch it because their mock navigation span had no op to tell it apart from a vital span.
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A restore starts a navigation span like any other, and redirect detection folds a navigation that follows another one closely into a child `navigation.redirect` span instead of a root one. A soft navigation is driven by a click, which is the same signal redirect detection reads as proof a navigation was user-initiated, so the two heuristics meet here. They agree: the click keeps the soft navigation out of the redirect path. Verified by swapping the click for a programmatic navigation of the same shape, which does get classified as a redirect and fails the test, so it is not passing vacuously.
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September 10, 2026 19:53
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Renames
webVitals.bfcachetowebVitals.bfcacheNavigationsand turns it on by default, so a back/forward-cache restore is measured like any other page view.Also adds e2e tests for the bfcache web vital reporting.